1. Field of the Invention
This invention relates to emulsion type adhesive compositions which include a metal neutralized copolymer, wherein the neutralized sulfonated copolymer has about 5 to about 250 meq. of neutralized sulfonate groups per 100 grams of the neutralized sulfonated copolymer, and less than about 200 parts by weight of a hydrogen resin of a petroleum or coal tar distillate, having about 5 to 6 carbon atoms, the hydrocarbon resin being composed of aliphatic dienes and monoolefins per 100 parts by weight of the neutralized sulfonated copolymer.
Broadly speaking, synthetic adhesives used in packaging can be classified into four categories: water based emulsion system, solvent based, reactive and hot melt adhesives. Of these four, currently the water based are used most extensively. Usually the water based adhesives are based on emulsion polymers and are applied to porous cellulosic substrates. Energy from the outside in some fashion is applied to the system to evaporate the water in order that a strong bond may be formed.
With the solvent-based adhesives usually a good wetting is achieved; however, their use has been becoming extremely restrictive due to expensive energy requirements for the evaporation of organic solvents, fire hazards associated with the use of these organic solvents and emissions problems with said solvents. The strict government environmental regulations and restrictions concerning worker's exposure to solvent vapors, etc. has placed extra pressure on the packager to use non-solvent based adhesives.
The hot melt adhesives are generally applied (as the name implies) by conventional extrusion or coating techniques in the temperature range of 250.degree. to 450.degree. C. on one of the surfaces to be bonded. The other surface is brought in contact with the hot surface for a sufficient period of time for the melt to cool, where upon solidification, a strong and durable bond is formed.
2. Prior Art
Several U.S. patents have described sulfonated polymers such as sulfonated Butyl and sulfonated EPDM in adhesive applications (e.g., U.S. Pat. No. 3,867,247 and U.S. Pat. No. 3,801,531). It is important to distinguish the instant invention over those prior art systems. The former patent are directed at a sulfonated butyl cement or EPDM terpolymer which is solvent based and is employed to laminate various substrates. It is important to note that the instant invention differs dramatically from these patents as follows:
(a) The adhesives of the instant invention are not deposited from solvents, but are water based emulsions;
(b) The instant invention may optionally include either a tackifier resin and/or plasticizer capable of associating with the neutralized sulfonate groups, and thereby reducing the melt viscosity of the resulting blends to make the systems more processable;
(c) The instant invention is directed to metal neutralized sulfonated elastomeric copolymers, whereas most of the prior art deals with sulfonated Butyl rubber (e.g., U.S. Pat. No. 3,867,247).